The present invention relates to gas generators used to inflate air bags in a vehicle occupant protection system and, more particularly, to an improved multiple-chamber gas generator containing an improved structure for isolating the propellant chambers of a multiple-chamber inflator so as to ensure proper deployment of the airbag.
Inflation systems for deploying an air bag in a motor vehicle generally employ a single gas generator in fluid communication with an uninflated air bag. A firing circuit typically triggers the gas generator when the sensed vehicle acceleration exceeds a predetermined threshold value, as through the use of an acceleration-responsive inertial switch. However, air bag inflation systems utilizing a single gas generator may be disadvantaged in that the onset pressurization/inflation rate is generally set to provide aggressive initial inflation in order to achieve a particular inflation time related to occupant position. An aggressive onset rate of pressurization may be problematic in situations where the occupant is out of position. Stated another way, rapid onset pressurization of the air bag may cause the air bag to impact against the occupant, thereby affecting the optimum kinematics of the occupant.
Consequently, multiple-chamber inflators have been developed which allow selective activation of either a single chamber or multiple chambers, depending on such factors as crash severity, occupant position sensing, and the weight and/or height of the occupant. Activation-of a single chamber provides softer deployment of the airbag, while simultaneous activation of multiple chambers provides the inflation force necessary to help prevent injury to heavier occupants of a vehicle. However, complete isolation of the propellant chambers of a multiple-chamber airbag inflator is critical to soft deployment of the airbag. It is also beneficial to facilitate an increase in pressure in an activated propellant chamber, because propellant residing in an enclosed chamber will bum more efficiently at higher chamber pressures.